1. Field of the Invention
The present invention relates to a brake device, which brings a braking element into contact with a disc rotating together with a wheel to thereby obtain a braking force, and in particular, to a brake device which has a release device for retracting the braking element from the disc.
The present application claims priority from Japanese Patent Application No. 2011-231885, filed Oct. 21, 2011, the entirety of which is hereby incorporated by reference.
2. Description of Related Art
In recent years, disc brakes are increasingly employed as brakes for railway vehicles because they do not require wear of the wheel to be considered, compared to a brake device of the type which presses a brake shoe directly against a wheel to obtain a braking force, and also they are capable of obtaining a stable braking force regardless of the state of the wheel. As a disc brake for a railway vehicle, there is known a type of disc brake in which a braking element is pressed in a direction toward the disc with the force of a mechanical spring, and it is moved in a direction to separate the two from each other by, for example, an actuator which uses hydraulic fluid pressure.
This type of a disc brake device is provided with a so-called fail safe function such that the braking force still functions with the pressing force of the mechanical spring even in a case where problems with fluid pressure supply occur.
Incidentally, a hydraulic disc brake device requires periodic oil maintenance due to oil leakage and so forth, and has problems with its serviceability. Consequently, it has been considered to use electricity rather than fluid pressure as the power source for disc brake devices for railway vehicles (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2010-25313).
However, in a state where fail safe is functioning, the braking force remains being applied to the wheel and it becomes difficult to move the vehicle. In particular, in comparison with a brake device that uses fluid pressure, in the case of a brake device that uses electricity, a transmission mechanism such as a decelerating mechanism intervenes between the output shaft of the electric motor and the shaft of the pressing piston that presses the braking element, and therefore, a conventional releasing mechanism cannot be simply used.